Disclosed herein is an apparatus and method that detects the travel direction of media in a media path in an image marking and fusing system that marks images onto print media substrates and fuses or fixes marked images onto the print media substrates.
Presently, in a typical electrophotographic printing process, a photoconductive member in a media marking engine is charged to a substantially uniform potential to sensitize a surface of the photoconductive member. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charges on the photoconductive member in irradiated areas. This process records an electrostatic latent image on the photoconductive member corresponding to informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact with the photoconductive member. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to media to generate unfused marked media. The media can include paper, a transparency, a substrate, or any other media.
After the media marking engine marks the media with the toner powder image, a fuser heats the toner particles to fuse the toner powder image to the media. While the fuser may take many forms, where heat or combination heat-pressure fusers are currently most common. One combination heat-pressure fuser includes a heat fusing roll in physical contact with a pressure roll. These rolls cooperate to form a fusing nip through which the unfused marked media passes. As the media passes through the rolls, heat and pressure fuses the powder image to the media.
Unfortunately, the unfused marked media may not travel in a media path at a desired angle from the media marking engine to the fuser. This can cause problems, such as edge wear, which is a critical problem in roll and belt fusing systems, such as in viton over silicone systems, Teflon over silicone systems, and other fusing systems. Edge wear can be the result of roller surface properties, the nature of media paper edges, the misalignment of media sheets as they pass through a fusing nip, and other properties. For example, shear stress is placed upon roller surfaces and paper surfaces when the surfaces conform around the edge of the media when it is in the fusing nip. Furthermore, if the media is not perfectly square to the rotation of the roll surface, a cutting or wiping action will occur. The cutting action exacerbates the wear of the roller surface and causes a resulting differential gloss and color differential on the media.
As a further example, in most conventional printing systems, the fuser is located in a machine frame on pins or slides that affect alignment control between the fuser roll axis and a machine paper path. In the fixed pinned system the misalignment between media motion and fuser roll axis is usually consistent, which results in more wear on one end of the fuser roll then the other. This is generally thought to be the side with the cutting motion. In slide systems the wear can be at either end depending upon the float of the system.
Furthermore, since the travel path of the media is dependent upon the skew adjustment performed at paper registration prior to marking, subsequent contact, transfer, stripping and transport alignments during marking and prior to fusing result in skew of the media travel direction. The skew of the media travel direction causes resulting issues of edge wear, cutting, wiping, gloss differential, and color differential mentioned above. These issues are especially problematic because current systems cannot detect the travel direction of unfused marked media.
Thus, there is a need for apparatus and method that detects the travel direction of media in a media path in an image marking and fusing system.